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Ilmenite is one of the common kimberlitic indicator minerals recovered during diamond exploration, and its distinction from non-kimberlitic rock types is important. This is particularly true for regions where these minerals are present in relatively low abundance, and they are the dominant kimberlitic indicator mineral recovered. Difficulty in visually differentiating kimberlitic from non-kimberlitic ilmenite in exploration concentrates is also an issue, and distinguishing kimberlitic ilmenite from those derive from other similar rocks, such as ultramafic lamprophyres, is practically impossible. Ilmenite is also the indicator mineral whose compositional variety has the most potential to resolve provenance issues related to mineral dispersions with contributions from multiple kimberlite sources.
Various published data sets from selected kimberlitic (including kimberlites, lamproites, and various ultramafic lamprophyres) and non-kimberlitic rock types have been compiled and evaluated in terms of their major element compositions. Compositional fields and bounding reference lines for ilmenites derived from kimberlites (sensu stricto), ultramafic lamprophyres, and other non-kimberlitic rock types have been defined primarily on MgO–TiO2 graphs as well as MgO–Cr2O3 relationships. 相似文献
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B. L. Turner II 《Geoforum》2002,33(4):427-429
Reviews and observations about the status of the discipline of geography, no matter how positive, invariably raise programmatic concerns. These concerns have a long history that arise from geography's struggles to find an identity that embraces its many parts and yet are consistent with the logic by which the academy partitions knowledge. Pedagogy and research historically claimed by geography is currently being reinvented and relabeled under such headings as “integrated environmental science” and “spatial science”, and these developments have the potential to change the breadth of the “geographic imagination”. Several observations about dominant explanatory perspectives and substantive domains of geographic enquiry are also provided. 相似文献
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Elsa Jullien Francis Grousset Bruno Malaiz Josette Duprat Maria Fernanda Sanchez-Goni Frdrique Eynaud Karine Charlier Ralph Schneider Aloys Bory Viviane Bout Jose Abel Flores 《Quaternary Research》2007,68(3):379-386
It has been proposed that tropical events could have participated in the triggering of the classic, high-latitude, iceberg-discharge Heinrich events (HE). We explore low-latitude Heinrich events equivalents at high resolution, in a piston core recovered from the tropical north-western African margin. They are characterized by an increase of total dust, lacustrine diatoms and fibrous lacustrine clay minerals. Thus, low-latitude events clearly reflect severe aridity events that occurred over Africa at the Saharan latitudes, probably induced by southward shifts of the Inter Tropical Convergence Zone. At a first approximation, it seems that there is more likely synchronicity between the high-latitude Heinrich Events (HEs) and low-latitude events (LLE), rather than asynchronous behaviours. 相似文献
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Kathleen O&#x;Reilly 《Geoforum》2006,37(6):958-972
In this paper, I analyze the connections made between women and water in a Rajasthani drinking water supply project as a significant part of drinking water’s commodification. For development policy makers, water progressing from something free to something valued by price is inevitable when moving economies toward modernity and development. My findings indicate that water is not commodified simply by charging money for it, but through a series of discourses and acts that link it to other “modern” objects and give it value. One of these objects is “women”. I argue that through women’s participation activities that link gender and modernity to new responsibilities and increased mobility for village women involving the clean water supply, a “traditional” Rajasthani woman becomes “modern”. Water, in parallel, becomes “new”, “improved” and worth paying for. Women and water resources are further connected through project staff’s efforts to promote latrines by targeting women as their primary users. The research shows that villagers applied their own meanings to latrines, some of which precluded women using them. This paper fills a gap in feminist political ecology, which often overlooks how gender is created through natural resource interventions, by concerning itself with how new meanings of “water” and “women” are mutually constructed through struggles over water use and its commodification. It contributes to critical development geography literatures by demonstrating that women’s participation approaches to natural resource development act as both constraints and opportunities for village constituents. It examines an under-explored area of gender and water research by tracing village-level struggles over meanings of latrines. 相似文献
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Sydney ABBEY 《Geostandards and Geoanalytical Research》1991,15(2):191-194
Using a recently published compilation of analytical data on reference samples SY-2, SY-3 and MRG-1 as an example, a case is presented in favor of more precise terminology in describing analytical methods used in reporting data in collaborative programs. The technique of final measurement in a particular method is often less important than earlier operations, such as sample attack or technique of separation. 相似文献
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R.N. Carver L.M. Chenoweth R.H. Mazzucchelli C.J. Oates T.W. Robbins 《Journal of Geochemical Exploration》1987,28(1-3)
Desert land surfaces are commonly characterized by a veneer or pavement of siliceous and/or ferruginous stony material. This material can be shown in most cases to be predominantly bedrock-derived, despite often severe modification by prolonged weathering, and can therefore be selectively sampled and analyzed as an indicator of bedrock geochemistry in geochemical surveys.Most pavements probably owe their existence to the interaction of several dispersion mechanisms. However, a common factor in all cases is the concentration of coarse particles at the surface as a result of the selective removal by erosion of fine dilutant material. Hence, the preferred name when used in the geochemical context is “lag”.In lag sampling, particles in the range 2.0–6.0 mm are screened on site from the unconsolidated surface material. Material in this size range has been found to be quite uniformly distributed over a wide range of arid region environments, including areas where residual soils are severely diluted by transported alluvial and aeolian materials.Data from exploration programmes for Au, Cu-Pb-Zn-Ba, and Ni allow comparison of results for lag sampling with those for alternative sample media in a variety of arid region environments. Analysis of lag samples for Au, Cu and As clearly indicates the presence of bedrock Au mineralization in the Paterson and Eastern Goldfields Provinces of Western Australia. In these areas both lags and soils exhibit good anomaly contrast, but lags show more extensive lateral dispersion, leading to advantages in reconnaissance exploration.Strong anomalies for Ni and Cu are developed in lags, compared with subdued response in fine-fraction soils over a Ni sulphide occurrence in the Eastern Goldfields which has been subjected to deep lateritic weathering.Lag geochemistry also clearly reflects sub-economic base metal and barite occurrences in the McArthur Basin, N.T., in spite of the dilution of surface soils by sands probably related to a Mesozoic marine incursion. Orientation sampling over a Pb-Zn prospect in the Pine Creek Geosyncline has demonstrated optimum response in lag samples compared with various size fractions of the associated lithosols.Variable dilution of lag samples by coarse quartz sand can be a problem in areas with substantial transported overburden. A simple procedure to ‘correct’ trace-element values using regression analysis based on the Fe content of samples is described as a means of reducing ‘noise’ resulting from such matrix variations. 相似文献
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M.R. St-Onge 《Tectonophysics》1981,76(3-4)
Three progressive metamorphic suites are developed in pelitic rocks of the northern Wopmay Orogen. Two suites are related to the Hepburn Batholith and one to the Wentzel Batholith. All three suites are cut by post-metamorphic wrench faults, some of which have significant vertical displacement. The structural relief so provided reveals that medium-and high-grade isograds associated with the Hepburn Batholith dip inward towards the batholith and are thus “hot-side-up”. Isograds associated with the Wentzel Batholith dip away from the batholith and are thus “hot-side-down”. It is concluded that Hepburn Batholith has the form of the flattened funnel fed from depth, and that Wentzel Batholith is the arched roof of an intrusive complex of unknown shape at depth. 相似文献
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K.C. Gyani 《Gondwana Research》1998,1(3-4):431-432
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A theory of two-dimensional geothermic problems is elaborated by the active temperature function at the vertical contact of two horizontally layered media. The approach offered before for oceanic ridges is extended to the case of continental margins and the upper part of a descending slab, i.e. “sink”, in island-arc areas. It is assumed that the plate motion in the oceanic area exists; in a descending area it is directed downward but remains zero on a continental side. Mathematically it symbolizes a “source—span—sink” thermal model. Numerical parameters are given for a theoretical thermal model of the heat-flow profile across the Kuril island arc, from the trench through Iturup Island, Sakhalin Island and the Tatarian Trough. 相似文献
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A lightly biodegraded crude oil from the Tolkinsk field (Upper Jurassic), situated in north-west Siberia, was found to contain a series of C28–C39 isoprenoid alkanes. Most of these components contain a pristane unit linked head-to-head with other isoprenoid units. The structures of these components were elucidated by mass spectral interpretations, comparisons with a synthesised standard and by reference to data published previously in the literature. These results extend the carbon number range, the variety of structural types, and the number of reported occurrences of these compounds in geological samples. These results provide further evidence for a contribution of bacterial cell-wall lipids to crude oils. 相似文献
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The National Geodetic Survey (N.G.S.) of the National Ocean Survey has undertaken a new project called POLar-motion Analysis by Radio Interferometric Surveying (POLA-RIS). The premier goal of the project is to establish a fully operational polar motion monitoring network, with a spatial resolution and accuracy of 10 cm and a temporal resolution of 24 hours. The new network will utilize radio interferometric techniques. The fixed POLARIS observatories may also serve as base stations to be used in conjunction with small-aperture, 3–10-m, mobile units for positional surveys for geodetic and geo-dynamic applications. The N.G.S. plans to cooperate fully with other governmental organizations having related responsibilities and interest in polar motion, earth rotation and geodynamics [e.g., National Aeronautics and Space Administration (NASA), United States Geological Survey (U.S.G.S.), United States Naval Observatory (U.S.N.O.)] as well as academic and private researchers. 相似文献